Glia constitute half of the brain's cellular mass, but relatively little is known of their physiological function. Recently, neurotransmitter receptors have been described on glia. We have shown that activation of receptors on astrocytes in primary cell culture and LRM55 glial cells results in the specific release of the inhibitory amino acid taurine. Beta-adrenergic, serotonin, and kappa-opiate agonists stimulate and substance-P inhibits release. Receptor-activated taurine release is a pereviously unrecognized glial cell function that may regulate neuronal activity. This proposal will address two aspects of glial release: (1) the mechanism responsible for taurine release and (2) the pathways that regulate receptor activated release. Primary cultures of astrocytes and LRM55 glial cells will be used. Primary cultures are a neuron-free preparation and will be used for detailed analysis of astrocyte function. LRM55 cells are a clonal cell line that express astrocytic properties. Experiments describing intracellular taurine distribution, Ca++ dependence of release, K+ depolarization stimulated release, equilibrium kinetics of release, and substrate specificity will be used to indicate if receptor mediated release occurs by a vesicular mechanism or is carrier mediated. Investigations of the pathways regulating release will focus first upon beta-adrenergic stimulated release. Then the pathways for opiate and substance-P receptors will be investigated. Studies will pharmacologically describe these receptors, describe interactions occurring as a result of simultaneous activation if more than one population of receptors, identify intracellular second messengers, and determine if serotonin, opiate and substance-P receptors regulate release via different or converging pathways affecting protein phosphorylation. Our results will establish that taurine release from glia is an integrated response and will provide mechanistic and pharmacological information required to test the hypothesis that glia are an integral regulatory component in pathways controlling neuronal activity.